The present invention relates to apparatus and a method for minimizing the amount of storage media required to contain vocalized speech. In particular the invention relates to real time silence detection/replay apparatus for monitoring an analog signal to detect and remove silent periods prior to recording the analog speech and for inserting the silence in synchronization on replay.
While many methods exist for reducing audio storage requirements via analog and/or digital compression and related encoding/decoding techniques, and while an encoding/decoding method similar to the present method was disclosed by Boies et al in IBM Technical Bulletin, Vol. 19, No. 6, November, 1976, pp. 2357-2358, the present method and apparatus are distinguishable in that instead of sampling a digitized (i.e. encoded) input, the present apparatus permits the direct sampling and editing of the received analog signal in parallel with receipt of the analog signal. Thus, producing a silence free output, independent of the encoding scheme (if any), and providing greater utility to the concept.
Additional distinctions in the apparatus can be found in the replay apparatus which on replay adjusts the level of the silent period to the ending level of the previous audio period, thereby preventing popping noises on replay. The silence detector is also distinguishable in that it continuously adjusts the level of the threshold envelope; performs numerous comparisons during each sampling period; and upon detecting a silent period, ensures that a sync and time code signal are inserted into the recorded speech so that upon replay the silent periods will occur in real time (i.e. with respect to total elapsed time from the initialization of the system) as opposed to delta time (i.e. with respect to the previous audio period). The silence detector is further distinguishable in that automatic gain control and background noise filters have been included to improve the performance of the silence detector.
Additional disclosures of specific "silence or stop" detecting means can be found in Thurston, U.S. Pat. Nos. 3,646,576 and 3,846,586 (i.e. selecting one of six outputs depending on the duration of the stop). Another minim detector that samples the number of times a minimum level is exceeded and that updates the threshold depending on the previous sample is taught in Araseki et al, U.S. Pat. No. 4,167,653. In particular Araseki discloses a speech detector with a threshold setting element containing an integrator for adjusting the threshold setting depending on the number of samples that have exceeded or been lower than the previously set threshold. Yet still another "silence latch" is disclosed in Dubnowski et al, U.S. Pat. No. 4,015,088 and which adaptively establishes the threshold level depending on an initial operating interval and a maximum level experienced over the interval or on operator choice.
Nowhere, however, is the present real time compaction technique and/or apparatus disclosed and which technique and apparatus permits real time compaction of speech, independent of whether the input speech signal is analog or digital. The technique and apparatus is further adaptable for use in conjunction with other known compression and encoding techniques to minimize the amount of storage media required to contain a given amount of speech.